1. Field of the Invention
The present invention relates to an apparatus and method of adjusting a head gap in an inkjet printer, and more particularly, to an apparatus and method of adjusting a head gap in an inkjet printer capable of automatically adjusting a gap between a sheet of paper and a printer head depending upon variations of sheet thickness.
2. Description of the Related Art
In general, an inkjet printer, as shown in FIG. 1, includes a printer head 30 having a nozzle 31 on a lower part thereof to jet ink, a carrier 20 having the printer head 30 mounted thereon, and chassis 10 to fix both ends of a carrier shaft 50 and a guide rail 11 to guide movements of the carrier 20. The carrier 20 is provided with a support bracket 51 and a guide slider 22 on its rear side so that the carrier 20 may move left and right along the carrier shaft 50 and the guide rail 11.
Accordingly, when a sheet of paper 40 picked up by a pickup roller (not shown) from a paper supply tray or cassette passes below the printer head 30 through a paper supply roller 60, the printer head 30 moves to the left and right along the carrier shaft 50 and the guide rail 11 by the carrier 20 and jets ink through the nozzle 31 for a printing operation. After the printing operation, the sheet of paper 40 is discharged through a paper discharge roller 70 and a paper discharge backup roller 80.
However, in general, such an inkjet printer as described above has a certain fixed distance between the nozzle 31 and the paper 40 below the printer head 30. Therefore, when the printer prints on envelopes or postcards, two to three times thicker than plain sheets of paper, the distance between the nozzle 31 and a thicker sheet of paper below the printer head 30 comes closer or uneven than that when printing on plain sheets of paper. In this case, ink may be blurred, causing a problem that deteriorates print resolutions.
In order to solve the above problem, a conventional inkjet printer is provided with a head gap adjuster 90 to adjust a gap between the paper 40 and a head depending upon a thickness of the paper 40. The head gap adjuster 90 has a carrier guide 21 provided on the guide slider 22 positioned on an upper part of the carrier 20, a cam 23 having a cam face to move the carrier guide 21 forwards and backwards, a compression spring 24 to compress the carrier guide 21 toward the cam 23, and a spring guide 25 to accommodate and support the compression spring 24.
When operating the head gap adjuster 90, the head gap adjuster 90 rotates the cam 23 in a direction of B to push the carrier guide 21 along the cam face in a case in which a head gap between the printer head 30 and a sheet is widened to print on envelops, post cards, etc.
At this time, the spring guide 25 is fixed to the carrier 20, so that the carrier guide 21 is biased in a direction of D due to a repelling force of the compression spring 24. However, the guide slider 22 elastically coupled to the carrier guide 21 is arranged not to move back and forth but to slide to the left and right along the guide rail 11, so that the guide slider 22 does not move and the spring guide 25 is pushed back by an eccentric amount of the cam face of the cam 23.
Accordingly, the spring guide 25 is pushed back so that the carrier 20 having the printer head 30 rotates in a direction of C about a rotation shaft of the carrier shaft 50, by which the carrier 20 is ascended in order for a front portion thereof, that is, a front portion of the nozzle 31 of the printer head 30, to be lifted about the carrier shaft 50.
Whereas, in the case that the gap between the printer head 30 and the sheet 40 is narrowed to print on normal sheets of paper, the cam 23 rotates in a direction opposite to the above, so that the carrier 20 is descended to the original position about the carrier shaft 50.
However, such a conventional inkjet printer as described above has a structure to lift up the front portion of the carrier 20 to widen and narrow the gap between the paper 40 and the printer head 30, causing a problem that the nozzle 31 of the printer head 30 is arranged skew with respect to the paper. In this case, a height difference occurs between both ends of the nozzle 31, causing a problem in that resolutions at the start and end positions where the nozzle 31 prints on the paper 40 become different.
Further, the conventional inkjet printer may be advantageous in that the gap between the printer head 30 and the paper 40 may be adjusted by a relatively simple structure thereof, but disadvantageous in that a user has to operate the cam 23 depending on the kinds of paper in order to adjust the head gap. In light of the above, the conventional inkjet printer becomes troublesome and inconvenient as well as causes the possibility of printer malfunctions.
In order to solve the above problem, as shown in FIG. 3, a head gap adjuster has been proposed in which both ends 50″ and 50′″ of a carrier shaft 50′ are structured in a shape of an eccentric cam having a certain eccentric amount δ, and a power transfer device driven by a separate driving motor is connected to the carrier shaft 50′, so that the carrier shaft 50′ rotates to descend and ascend a carrier 20′, thereby to adjust a gap between a print head 30′ and a sheet of paper 40′ by rotating the carrier shaft 50′. However, the adjuster employs an extra driving motor and a power transfer device, causing a problem in that manufacture cost increases as well as the printer size becomes bigger since space in which the extra driving motor and the power transfer device are installed must be secured.
Further, the head gap adjuster does not have a sensor to detect the head gap states (e.g., a ‘narrow’ position or ‘wide’ position). Thus, a controller for the printer would not recognize a current head gap state when the printer is turned on.
Accordingly, every time power is turned on, the printer sets an initialization gap, for example, to the ‘narrow’ position by performing a head gap initialization process to set a current head gap state, and then adjusts a specific head gap as required.
As stated above, every time the printer is turned on, the conventional head gap adjuster performs the head gap initialization process to set an initialization gap to the ‘narrow’ position, causing a problem in that an initial arrangement time period to print becomes longer and noise generated due to the head gap initialization process is added to the printer.